??? operator in swift.

or_throw.swift

infix operator ???

func ???<T> (_ value: @autoclosure () -> T?, _ error: @autoclosure () -> Error) throws -> T {
    guard let value = value() else {
        throw error()
    }
    return value
}

do {
  let value = Optional(20) ??? NSError()
  print(value)
} catch {
  print(error)
}